Thin-film transistors and other three-port semiconductor devices typically include gate, source and drain electrodes. A semiconductive thin-film channel is disposed between the source electrode and drain electrode. The transistor also includes a dielectric insulator physically separating the gate electrode from the channel, and from the source electrode and the drain electrode. The semiconductive channel provides an electrical pathway between the source and drain electrodes having controllable conductive properties. In particular, the voltage applied to the gate electrode causes the conductive properties of the channel to vary. Specifically, the applied gate voltage controls the ability of the channel material to permit charge transport through the channel material between the other two electrodes (e.g., a source electrode and drain electrode). The electrical properties of the various materials used in the thin-film transistor determine the threshold voltage required to turn on the transistor and induce a conductive pathway between the source and drain electrodes.